JP5741203B2 - Manufacturing method of organic EL element - Google Patents

Description

  The present invention relates to an organic EL display element, and more particularly to a method for manufacturing an organic EL element that is driven at a low voltage and has a high efficiency as the element capacity of the display element increases.

  Organic EL elements used in vehicles are required to have high reliability and low power consumption drive even in a wide range of environments. Low voltage and high current efficiency of organic EL elements are important. It has become a challenge.

  As a method for achieving low voltage driving, an electron transport layer having high electron mobility or an electron transport material having a low LUMO (Lowest Unoccupied Molecular Orbital) is applied, and an electron injection barrier from the cathode is reduced. Low voltage drive is achieved by making it small, but if the electron transport material having the above high mobility or the electron transport material having a small LUMO is employed, the number of electrons becomes excessive and the hole transport layer deteriorates. There was a problem that the lifetime was shortened.

  In addition to the above method, regarding the low voltage driving of the organic EL element, as in Patent Document 1, the organic layer in the portion in contact with the cathode electrode is alkali metal ion, alkaline earth metal ion, rare earth metal ion. Those composed of a mixed layer of an organometallic complex compound containing at least one of the above and a charge transporting organic compound are known.

JP 2000-182774 A

However, even the method as disclosed in Patent Document 1 has a problem in that when the organometallic complex compound is mixed with a high mobility material or an electron transport material having a small LUMO, the driving voltage does not decrease but increases. It was. Furthermore, changing the material configuration of the organic EL element requires various parameters to be examined in order to obtain appropriate element characteristics, and an optimal structure must be selected, which takes time for development.
In addition, the organic EL element is a self-luminous element, and burn-in has been an issue. However, as a method of reducing initial deterioration of energization, the element structure and materials are changed to improve the element life. There is a problem that cannot be improved.

  Therefore, in view of the above-described problems, the present invention provides a method for manufacturing an organic EL element that can suppress a driving voltage low and easily improve current efficiency without changing the material or structure of the organic EL element. The purpose is to do.

In order to solve the above-described problems, the present invention provides a method for manufacturing an organic EL element in which at least an organic layer is sandwiched between a pair of electrodes, wherein the first organic EL element is formed. Applying a reverse bias to the organic EL element after the process or applying a reverse bias while performing heat treatment increases the element capacity of the organic EL element in a range of 1.5% to less than 3.4% . This is a method for producing an organic EL device having two steps, and the drive voltage can be kept low and the current efficiency can be easily improved without changing the material and structure of the organic EL device.

  In the present invention, the second step is a step of applying a reverse bias to the organic EL element.

  According to a third aspect of the present invention, the second step is a step of heat-treating the organic EL element. According to the second step of the second and third aspects, the driving voltage is added without adding a step to the aging treatment. And the current efficiency can be easily improved.

  Provided is a method for manufacturing an organic EL element that can suppress a drive voltage low and easily improve current efficiency without changing the material and structure of the organic EL element.

It is the (a) front view and the (b) sectional view showing the organic EL element concerning the embodiment of the present invention. It is sectional drawing of the layer which comprises the organic EL element which concerns on the said embodiment. It is a graph which shows the relationship between the relative capacity | capacitance of the organic EL element of the Example of this invention, and a voltage change (initial luminance 3000cd / m < ² >). It is a graph which shows the relationship between the relative capacity | capacitance of the organic EL element of the Example of this invention, and a voltage change (initial luminance 32000cd / m < ² >). It is a graph which shows the relationship between the relative capacity | capacitance of the organic EL element of the Example of this invention, and a brightness | luminance lifetime (LT95). It is a graph which shows the relationship between the relative capacity | capacitance of the organic EL element of the said Example, and the relative luminance after 150-hour drive. It is a graph which shows the relationship between the relative capacity | capacitance of the organic EL element of the said Example, and the voltage change after 150-hour drive.

  Hereinafter, embodiments in which the present invention is applied to a dot matrix type organic EL element 100 will be described with reference to the accompanying drawings.

  In FIG. 1, an organic EL element 100 includes a supporting substrate 1, a first electrode (anode) 2, an insulating layer 3, a partition wall 4, an organic layer 5, a second electrode (cathode) 6, a sealing member. It is mainly composed of the member 7.

  The support substrate 1 is a translucent glass substrate having a rectangular shape.

The first electrode 2 is formed in a layer shape on a support substrate 1 by a method such as sputtering or vapor deposition using a light-transmitting conductive material such as ITO (Indium Tin Oxide), and is patterned in a stripe shape by a photolithography method, for example. The surface is subjected to surface treatment such as UV / O ₃ treatment or plasma treatment.

  The insulating layer 3 is made of an insulating material such as polyimide or phenol, and is formed in a predetermined shape on a non-light emitting portion on the support substrate 1 by means such as photolithography. The insulating layer 3 is formed between the first electrode 2 and slightly overlaps the first electrode 2, and insulates the first electrode 2 from the second electrode 6.

  The partition wall portion 4 is made of, for example, an insulating material such as a phenol-based material, and the cross section is formed in, for example, a reverse taper shape by means such as photolithography. The partition wall 4 is formed on the first electrode 2 and the insulating layer 3 so as to intersect the first electrode 2 at a substantially right angle, and at a position corresponding to a second electrode (cathode) 6 described later on the support substrate 1. As shown in FIG. 1 (a), it is formed so as to have an arc shape when viewed from the laminated body forming surface side of the support substrate 1.

  The organic layer 5 is formed on the first electrode 2 and the insulating layer 3, and as shown in FIG. 2, a hole injection transport layer 51, a first light emitting layer 52, a second light emitting layer 53, The electron transport layer 54 and the electron injection layer 55 are sequentially laminated by means such as a vapor deposition method to form a layer having a thickness of about 60 to 150 nm.

The hole injecting and transporting layer 51 has a function of taking holes from the first electrode 2 and transmitting them to the first and second light-emitting layers 52 and 53, and has a high hole mobility such as an amine compound. The transporting material is formed in a layer shape having a film thickness of about 15 to 40 nm by means such as vapor deposition. The hole transporting material has a glass transition temperature of 85 ° C. or higher (more preferably 130 ° C. or higher), a hole mobility μ _h of about 4 × 10 ⁻⁴ cm ² / V · s, and an energy gap. Is about 3.1 eV.

As shown in FIG. 2, the first light-emitting layer 52 includes a first dopant material 52a as a light-emitting material and a second dopant material 52b as a hole transport material in a first host material 52c. To form a layer having a film thickness of 20 to 60 nm.
The first host material 52c is capable of transporting holes and electrons, and has a function of emitting light when the holes and electrons are transported and recombined. For example, the first host material 52c is made of a distyrylarylene derivative or anthracene derivative. Become.
The first dopant 52a has a function of emitting amber (orange) light in response to recombination of electrons and holes, so that the doping amount of the first dopant 52a does not cause concentration quenching. For example, the first dopant 52a is added so that the concentration in the first light emitting layer 52 is 2 to 8%. Further, ionization potential _{I p} of the first dopant 52a has a lower value than 0.1eV than the ionization potential _{I p} of the first host material 52c.
The second dopant 52b, the hole mobility is higher electron mobility has a lower hole-transport properties, the hole mobility mu _h is in the 10 -4 ^{cm 2 /} V · ^s or more. Moreover, the 2nd dopant 52b is added so that the density | concentration in the 1st light emitting layer 52 may be 5-50%.

As shown in FIG. 2, the second light-emitting layer 53 includes a second dopant 53a as a light-emitting material and a fourth dopant 53b as a hole-transporting material in the second host material 53c. To form a layer having a film thickness of 20 to 60 nm.
The second host material 53c can transport holes and electrons, and has a function of emitting light when the holes and electrons are transported and recombined. For example, the second host material 53c is made of a distyrylarylene derivative or anthracene derivative. Become.
The third dopant 53a has a function of emitting blue light in response to recombination of electrons and holes, and the third dopant 53a may be configured so that the doping amount of the third dopant 53a does not cause concentration quenching. Desirably, for example, the third dopant 53a is added so that the concentration in the second light emitting layer 53 is 2 to 8%. Further, ionization potential _{I p} of the third dopant 53a has a lower value than 0.1eV than the ionization potential _{I p} of the second host material 53c.
The fourth dopant 53b has a hole transport property with a high hole mobility and a low electron mobility, and the hole mobility is 10 ⁻⁴ cm ² / V · s or more. The fourth dopant 53b is added so that the concentration in the second light emitting layer 53 is 5 to 50%.

The electron transport layer 54 has a function of transmitting electrons to the first and second light-emitting layers 52 and 53. For example, an electron transport material such as aluminum quinolinol (Alq ₃ ) that is a chelate compound is deposited by a vapor deposition method or the like. It is formed in a layered form having a film thickness of about 8 to 30 nm by means. Alternatively, an organic material having an electron mobility of 1 × 10 ⁻⁶ cm ² / V · s or less is used.

  The electron injection layer 55 has a function of injecting electrons from the second electrode 6, and is formed, for example, by forming lithium fluoride (LiF) into a layer having a thickness of about 0.5 nm by means such as a vapor deposition method. The electron injection layer 55 may be lithium quinoline (Liq).

  The second electrode 6 is formed by forming a conductive material such as aluminum (Al) or magnesium silver (Mg: Ag) into a layer having a thickness of about 50 to 200 nm by means such as vapor deposition. Is cut into stripes.

  As described above, the first electrode 2, the organic layer 5, and the second electrode 6 are sequentially laminated on the support substrate 1 to obtain an organic EL element. Each of the organic EL elements is arranged in a matrix and becomes each light emitting pixel constituting the light emitting display section.

  The sealing member 7 is formed by forming a molded glass or flat plate member made of, for example, a glass material into a concave shape by an appropriate method such as sandblasting, cutting, and etching. The sealing member 7 is hermetically disposed on the support substrate 1 via an adhesive 71 made of, for example, an ultraviolet curable epoxy resin, so that the light emitting display unit is sealed between the sealing member 7 and the support substrate 1. Stop. The sealing member 7 is configured to be slightly smaller than the support substrate 1 so that the end of the first electrode 2 and the end of the second electrode 6 are exposed to the outside. The sealing member 7 may have a flat plate shape. In this case, the sealing member 7 is disposed on the support substrate 1 via a spacer.

  As described above, the dot matrix type organic EL element 100 having the light emitting display portion is obtained. In the organic EL element 100, holes from the first electrode 2 and electrons from the second electrode 6 are recombined in the first and second light-emitting layers 52 and 53, whereby orange light emission and blue light emission. Thus, white light is emitted from the first electrode 2 side by mixing these colors. Further, the organic EL element 100 selects either one of the plurality of first electrodes 2 and the plurality of second electrodes 6 formed in a stripe shape and applies a constant current, and selects the selected first electrode 2 and second electrode 2. Light emission is driven by so-called passive drive, in which a light emitting pixel corresponding to a position opposite to the electrode 6 emits light.

  In addition, the organic EL element 100 of the present embodiment has a configuration in which the hole injection / transport layer 51 is formed between the first electrode 2 and the organic layer 5, but the first electrode 2 and the organic layer 5 A hole injection layer and a hole transport layer may be sequentially stacked between the layers.

  In this embodiment, the host material of the first light emitting layer 52 and the second light emitting layer 53 is a single material, but it may be composed of a plurality of materials.

  In the present embodiment, the electron transport layer 54 is formed of a single layer, but may be formed of a plurality of layers.

  In this embodiment, the organic layer 5 is composed of two layers of the first light-emitting layer 52 and the second light-emitting layer 53. However, an element configuration that emits monochromatic light in one layer may be used.

  From this, the description of the 1st process and the 2nd process in the manufacturing method of the organic EL element 100 of this invention, and Examples 1 thru | or 13 which measured the relative brightness | luminance and voltage change after implementing the 2nd process of this invention, and Comparative example 1 will be described in detail.

(First step)
The transparent electrode 1 is formed by forming 80 nm of ITO and then forming 30 nm of HT1 as the hole injecting and transporting layer 51.
The first light-emitting layer 52 has EM1 (I _p = 5.9 eV, Ea = 2.9 eV, μ _e = 3 × 10 ⁻³ cm ² / V · s, μ _h = 2 × 10 ⁻ as a host material 52c. ³ cm ² / V · s, T _g = 130 ° C.), orange dopant AD1 (Eg = 2.0 eV, Ip = 5.2 eV) as the first dopant 52a, and HT1 as the hole transport material 52b (T _g = 132 ° C., I _p = 5.4 eV, μ _h = 4 × 10 ⁻⁴ cm ² / V · s), and the ratio of EM1: AD1: HT1 was 6: 1.2: 6. One light emitting layer 52 is formed.

The second light emitting layer 53 uses EM1 as the host material 53c, and blue green dopant BD1 (E _g = 2.7 eV, I _p = 5.6 eV, T _g = 200 ° C.) as the second dopant 53a. The second light emitting layer 53 is formed by using HT1 as the hole transport material 53b and EM1: BG1: HT1 at 20: 1.2: 10.
As the electron transport layer 54, ET1 (I _p = 5.8 eV, E _a = 3.0 eV, μ _e = 5 × 10 ⁻⁶ cm ² / V · s, T _g = 176 ° C.) of 10 nm, the electron injection layer 55 LiF is formed to 1 nm, and Al is formed to 100 nm as the cathode 6.

The characteristics of the organic EL element obtained are as follows: peak luminance L _p = 3000 cd / m ² , driving voltage V ₀ = 5.13 V, current efficiency L / J ₀ = 10.32 cd / A, and element capacitance C ₀ = 1. It was 306 nF (area; 2 × 2 mm).

(Second step)
When the organic EL element formed in the first step was subjected to a reverse bias electric field of 2.14 × 10 ⁶ V / cm for 1 hour in an environment of 30 ° C., the element capacitance C ₁ = 1.307 nF (capacitance ratio C ₁ / C ₀ = 1.001 (0.1% increase in device capacity)), drive voltage V ₁ = 5.1 V (drive voltage ratio V1 / V ₀ = 0.98), L / J ₁ = 13.03 cd / A ( _{L1J 0 / L 0 J 1 =} 1.02) to become.

Hereinafter, the measurement results of the voltage change and the current efficiency change of the organic EL elements (Examples 1 to 13 and Comparative Example 1) on which the second step was similarly performed are summarized in Table 1.

3 and 4 are graphs showing the results of Table 1 above. FIG. 3 shows the voltage change V / V by causing the organic EL elements of Examples 1 to 13 and Comparative Example 1 to emit light at a luminance of 3000 cd / m ^2. it is a graph of V ₀ and the current efficiency change L / _{L 0.} Based on the increase in device capacitance (relative capacitance C / C ₀ is 1 or more), the voltage change V / V ₀ decreased and the current efficiency change L / L ₀ increased.
FIG. 4 is a graph obtained by measuring voltage change V / V ₀ and current efficiency change L / L ₀ when the organic EL elements of Examples 1 to 13 and Comparative Example 1 are driven at high luminance (32000 cd / m ² ). Thus, the same result as in normal driving (luminance 3000 cd / m ² ) was obtained.
Therefore, the organic EL element 100 formed in the first step is increased in element capacity by performing the second step as in the present invention without changing the material or structure, so that the driving voltage of the organic EL element can be increased. It can be kept low and current efficiency can be easily improved.

Since it is desired that the voltage change is reduced by 5% or more in low voltage driving and the current efficiency change is increased by 10% or more in order to improve the current efficiency, the device capacity is 1. It is preferable to increase it by 4% or more. Further, when the element capacity is increased to 3.4% as in Comparative Example 1, the drive voltage increases such that the voltage change V / V ₀ is 1.3 and the current efficiency change L / L ₀ is 0.53. , Current efficiency decreases. These element capacities need to be optimized depending on the material and configuration of the organic EL element.

  Next, the long lifetime of the organic EL device in which the second step has been performed in the same manner will be described using Examples 14 to 17 and Comparative Examples 2 and 3.

In Example 14, when the organic EL element formed in the first step of Example 1 was subjected to a reverse bias electric field of 2.14 × 106 V / cm for 1 hour in an environment of 110 ° C., the capacity ratio C ₁ / C ₀ = 1.025 (2.5% increase in element capacity)), and LT95 (time until 5% decrease in luminance from the initial luminance) when the element subjected to this process is DC current driven at an initial luminance of 3000 cd / m ² is 170 hours, the relative luminance L / L0 of the organic EL element after driving for 150 hours was 0.95, and the increase value ΔV of the driving voltage was 0.12V.

Table 2 below summarizes the measurement results of the luminance life, relative luminance after driving for 150 hours, and voltage change of the organic EL elements (Examples 14 to 17 and Comparative Examples 2 and 3) that were similarly subjected to the second step.

5 to 7 are graphs showing the results of Table 2 above, and FIG. 5 is a graph showing the luminance lifetimes of the organic EL elements of Examples 14 to 17 and Comparative Examples 2 and 3. FIG. It can be seen that Examples 14 to 17 have a longer luminance life (LT95) than Comparative Examples 2 and 3.
FIG. 6 is a graph obtained by measuring the relative luminance of the organic EL elements of Examples 14 to 17 and Comparative Examples 2 and 3 after driving for 150 hours. In Examples 14 to 17, the relative luminance after driving for 150 hours is larger than those of Comparative Examples 2 and 3.
FIG. 7 is a graph obtained by measuring voltage changes after driving for 150 hours for the organic EL elements of Examples 14 to 17 and Comparative Examples 2 and 3. In Examples 14 to 17, the voltage change after 150 hours of driving is smaller than in Comparative Examples 2 and 3.
Therefore, the lifetime of the organic EL element 100 can be easily increased by increasing the element capacity by carrying out the second process as in the present invention without changing the material or structure of the organic EL element formed in the first process. Can be improved.

  In order to reduce the voltage change after 150 hours, it is preferable to increase the element relative capacity by 1.5% or more in the configuration of the organic EL element of the example. It is necessary to optimize the system and configuration.

100 Organic EL element 1 Support substrate 2 First electrode (anode)
3 Insulating layer 4 Partition 5 Organic layer 6 Second electrode (cathode)
7 sealing member 51 hole injection transport layer 52 first light emitting layer 52a first dopant 52b second dopant 52c first host material 53 second light emitting layer 53a third dopant 53b fourth dopant 53c second Host material 54 Electron transport layer 55 Electron injection layer 71 Adhesive

Claims (1)

A method of manufacturing an organic EL element having at least an organic layer sandwiched between a pair of electrodes, wherein a reverse bias is applied to the organic EL element or a heat treatment is performed after the first step of forming the organic EL element. However, the manufacturing method of the organic EL element characterized by having the 2nd process which increases the element capacity of the said organic EL element in 1.5% or more and less than 3.4% by applying a reverse bias .

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